The David A. Johnston Cascades Volcano Observatory (CVO) is a volcano observatory in the US that monitors volcanoes in the northern Cascade Range. It was established in the summer of 1980, after the eruption of Mount St. Helens. The observatory is named for United States Geological Survey (USGS) volcanologist David A. Johnston, who was swept away in the Mount St. Helens eruption on the morning of May 18, 1980. The observatory's current territory covers Oregon, Washington, and Idaho. The Cascade Range's extent includes northern California, and Cascade volcanoes in that state, such as Mount Shasta and Lassen Peak, previously fell under the CVO's jurisdiction. However, these volcanoes now fall under the jurisdiction of the California Volcano Observatory (CalVO), formed in February 2012 and based in Menlo Park, California, which monitors and researches volcanic activity throughout California and Nevada.

The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as many of those in the North Cascades, and the notable volcanoes known as the High Cascades. The small part of the range in British Columbia is referred to as the Canadian Cascades or, locally, as the Cascade Mountains. The highest peak in the range is Mount Rainier in Washington at 14,411 feet (4,392 m).